Hydration of thiourea and mono-, di-, and tetra-N-alkylthioureas at infinite dilution: a thermodynamic study at a temperature of 298.15 K

Molar enthalpies of solution in water, ΔsolHm, of thiourea, methylthiourea, ethylthiourea, dimethyl-1,3-thiourea, diethyl-1,3-thiourea, and tetramethyl-1,1,3,3-thiourea were measured at T = (296.84, 302.45, and 306.89) K by isothermal calorimetry. Experimental results were used to derive molar enthalpies of solvation at infinite dilution (i.d.), ΔsolvHm∞, changes in heat capacity due to the solution process, ΔsolCp,m∞, and partial molar heat capacities at i.d., Cp,2∞, at T = 298.15 K. The methylene group contributions to the enthalpy of solvation and partial molar heat capacity were −4.5 kJ·mol–1 and 88.5 J·K–1·mol–1, respectively, in good agreement with our earlier data for N-alkylureas and the literature data for various homologous series of alkyl-substituted compounds. The contributions of the functional groups to both ΔsolvHm∞ and Cp,2∞ were derived by employing additive schemes and compared with our earlier data for urea and corresponding N-alkylureas. Hydration behavior at the i.d. of thiourea, urea, and corresponding N-alkyl derivatives were compared and discussed.